When your dick's size becomes so large that it reaches a critical mass and begins to collapse in on the balls. The dick then retracts inside of the pelvis and forms a psuedo vagina.

"Hey Bobby what's that glowing rod coming from your pants?!" "Oh thats just a dick implosion, an interstellar mass larger than the sun retreating back into itself so as to hide its awesomeness from the world because the world cannot understand it yet."